Temporary air stripping system was operated from April to September 1997 as emergency response measure:
- Five-tray stripper designed to treat water from the clear well; system flow rate was 250 gallons per minute (gpm).

Permanent air stripping system was installed in September 1997 and is still in operation:
- Two packed air stripping towers, each 33 feet tall by 6 feet in diameter, operated in series
- Packed with 2-inch Jaeger Tri-pack filled to 21 feet; design air to water ratio of 150:1; design flow rate is 480 gpm for MTBE influent concentrations of up to 1,000 ug/L
- First tower is designed to remove MTBE to levels below 20 ug/L; the second tower is used to polish the water.
- Each tower is equipped with a blower designed to circulate 10,000 cubic feet per minute (cfm) of air
- Influent to first tower is softened with lime and settled; effluent from the second tower is pumped through a sand and anthracite filter prior to entering the distribution system

Contaminants:MTBE, BTEX, TPH
- MTBE concentrations as high as 1,050 ug/L in public water supply wells

Waste Source:Leaks from underground storage tanks

Type/Quantity of Media Treated:Drinking Water

Purpose/Significance of Application:Use of air stripping to treat MTBE in drinking water

Regulatory Requirements/Cleanup Goals:
The treatment goal for MTBE is 10 ug/L in the effluent from the air stripping system

Results:Temporary Stripper - During five months of operation, MTBE influent levels of 200-600 ug/L were reduced to concentrations ranging from 17-375 ug/L, an average reduction of 40 percent.
Permanent System - From September 1997 through September 1999, MTBE effluent concentrations were consistently below the treatment goal of 10 ug/L (about 93% of the time), and were below the detection limit of 0.2 ug/L almost 30 percent of the time. The average percent reduction in MTBE concentrations was 83% after the first stripper tower and 95% after the second stripper tower.

Cost Factors:The total capital cost for the packed tower system was $185,000. The operation and maintenance costs are $30,000 per year. The treatment system is operated by city personnel. No costs were provided for the temporary air stripping system.

Description:The city of LaCrosse operates a drinking water treatment plant that provides water for the city's residents. The plant treats approximately 300 gallons per minute (gpm) in the winter and 450 gpm in the summer. In April 1997, two LaCrosse PWS wells were found to be contaminated with MTBE, BTEX, and other petroleum hydrocarbons. The source of the contamination was determined to be leaking underground storage tanks (UST) at three gasoline service stations. found in the wells. In April 1997, as an emergency response measure, a temporary air stripping system for treating MTBE was installed to allow the wells to continue to be used as the city's water supply source. The permanent air stripping system was installed in September 1997 and is still in operation. The system includes two packed air stripping towers, each 33 feet tall by 6 feet in diameter, operated in series.

During the first two years of operation, the dual packed tower air stripping system at the LaCrosse treatment plant has consistently reduced MTBE concentrations in the source wells to below the cleanup goal of 10 ug/L. There have been no exceedances of the cleanup goal during the last 12 months of operation. According to the State, the stripping system appears to be less efficient during extremely cold weather. Ambient air is pulled from outside the building into the air stripper blowers with no preliminary heating process. The total capital cost for the packed tower system was $185,000, with annual operation and maintenance costs of $30,000. No significant operation or maintenance problems have been reported and there have been no problems with fouling or scaling to date.